The present invention relates to a semiconductor module with a base board and a side board in intersecting planes and to a conductor on a conductive path extending between the base board, and the side board, and the invention particularly relates to assurance of required dielectric strength between the adjacent boards of the semiconductor module.
Semiconductor modules in which one or more semiconductor chips, particularly high-power semiconductor chips, are installed in a housing which is developed in such a manner that heat loss produced in the semiconductor chips can be discharged in optimal fashion to the surrounding, are manufactured and used in large numbers. If the semiconductor chips are to be electrically insulated from their surroundings, a base plate of a ceramic material, for instance aluminum oxide, aluminum nitride, beryllium oxide, etc. is frequently used. The required conductive paths, etc. are produced on the surface thereof. In this connection, copper sheets which are fastened to the ceramic boards by the so-called direct bonding process have proven particularly satisfactory.
If only a few semiconductor chips are combined in a module, a simple, economical construction which is very dependable in operation is obtained. However, as soon as a larger number of semiconductor chips are to be combined in a module, and particularly when these chips are at least in part controllable semiconductor elements such as thyristors, transistors, etc., crossings of the conductive paths are necessary, for which, to be sure, for the feeding of current to the control electrodes of the controllable semiconductor elements, lines of small cross section are sufficient. But, they however must be insulated and fixed in suitable manner in order to avoid damage or short circuits.
Examples of the complicated production of conductive paths which extend in a second plane are given in Federal Republic of Germany Patent 31 37 570. The second plane of the conductor path is formed by pre-shaped wires and sheets which are mounted and soldered by hand. It is obvious that the reliability is decreased as a result of the large number of solder points, and the cost of manufacture increased.
Another method of producing crossings in the case of copper conductive paths which are connected to a ceramic substrate by the direct bonding process is known from U.S. Pat. No. 4,500,029. In that method, parts of the copper sheets are prevented by suitable coatings from bonding to the ceramic substrate and/or other copper sheets. This method is extremely difficult in actual practice. The crossings are mechanically unstable since the copper becomes soft as a result of the heat treatment. In many cases, the crossings produced do not have the desired insulating action.